Block copolymer and composition thereof

ABSTRACT

Disclosed is a block copolymer comprising at least two S polymer blocks comprising vinyl aromatic hydro-carbon monomer units, and one B polymer block or two or more B polymer blocks which contains or collectively contain isoprene monomer units and 1,3-butadiene monomer units, wherein the amount of the vinyl aromatic hydrocarbon monomer units and the total amount of the isoprene monomer units and the 1,3-butadiene monomer units are, respectively, from 60 to 95% by weight and from 40 to 5% by weight, each based on the weight of the copolymer, wherein the isoprene monomer unit/1,3-butadiene monomer unit weight ratio is from 45/55 to 97/3, and wherein the vinyl aromatic hydrocarbon monomer unit moiety of the copolymer has a short segment ratio of from 0 to 30% by weight, which is defined as the weight percentage, based on the total weight of vinyl aromatic hydrocarbon monomer units in the copolymer, of the vinyl aromatic hydrocarbon monomer units in at least one short segment consisting of 1 to 3 vinyl aromatic hydrocarbon monomer units.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a block copolymer. Moreparticularly, the present invention is concerned with a block copolymercomprising at least two S polymer blocks, each comprising vinyl aromatichydro-carbon monomer units, and one B polymer block or two or more Bpolymer blocks which contains or collectively contain isoprene monomerunits and 1,3-butadiene monomer units, wherein the amount of the vinylaromatic hydrocarbon monomer units, the total amount of the isoprenemonomer units and the 1,3-butadiene monomer units, and the isoprenemonomer unit/1,3-butadiene monomer unit weight ratio are withinrespective specific ranges, and wherein the vinyl aromatic hydrocarbonmonomer unit moiety of the block copolymer has a short segment ratiowithin a specific range, the short segment ratio being defined as theweight percentage, based on the total weight of vinyl aromatichydrocarbon monomer units contained in the block copolymer, of the vinylaromatic hydrocarbon monomer units contained in at least one shortsegment consisting of 1 to 3 vinyl aromatic hydrocarbon monomer units.The block copolymer of the present invention has excellent thermalstability in that, even when the blocks copolymer is heated at hightemperatures, the change in the molecular weight distribution of theblock copolymer due to crosslinking or breakage of polymer chains of theblock copolymer can be suppressed. Therefore, even when the blockcopolymer is subjected to shaping at high temperatures, occurrence ofgelation can be suppressed. By virtue of the above-mentioned excellentthermal stability of the block copolymer, a shaped article (such as asheet) produced from the block copolymer is free from marked occurrenceof fish eyes (hereinafter, a “fish eye” is frequently referred to simplyas a “FE”). Further, the shaped article has excellent stiffness,elongation, impact resistance, transparency and heat shrinkability.Accordingly, the block copolymer of the present invention can beadvantageously used for producing various shaped articles. The presentinvention is also concerned with a block copolymer/styrene resincomposition comprising the block copolymer and a styrene resin in aspecific ratio.

[0003] 2. Prior Art

[0004] A block copolymer comprising vinyl aromatic hydrocarbon monomerunits and conjugated diene monomer units (such as a 1,3-butadienemonomer unit) wherein the vinyl aromatic hydrocarbon monomer unitcontent is relatively high, has various excellent characteristics, suchas transparency and impact resistance, so that the block copolymer hasbeen used for producing injection-molded products, extrusion-moldedproducts (such as a sheet and a film) and the like. Further, acomposition comprising the block copolymer and a styrene polymer hasexcellent transparency and mechanical properties, so that thecomposition has been used for producing a sheet, a film and the like.

[0005] With respect to the block copolymer and the composition, a numberof proposals have been made in patent documents. For example, in anattempt to improve the transparency and impact resistance of a blockcopolymer, Unexamined Japanese Patent Application Laid-OpenSpecification No. 52-58788 (corresponding to U.S. Pat. No. 4,167,545)discloses a branched block copolymer comprising a vinyl aromatichydrocarbon and 1,3-butadiene, which is obtained by division-wise addinga catalyst to a block copolymerization system. Unexamined JapanesePatent Application Laid-Open Specification No. 53-8688 (corresponding toU.S. Pat. No. 4,120,915) attempts to obtain a block copolymer having animproved thermal stability by a method comprising polymerizing a vinylaromatic hydrocarbon to obtain a vinyl aromatic hydrocarbon polymer,followed by addition of 1,3-butadiene and a small amount of isoprene toperform a coupling reaction. In an attempt to improve the impactresistance of a block copolymer, Unexamined Japanese Patent ApplicationLaid-Open Specification No. 2-113007 discloses a block copolymercomprising a vinyl aromatic hydrocarbon polymer block and a polymerblock composed mainly of isoprene, which has a specific blockconfiguration. For the purpose of obtaining a thermoplastic polymercomposition having excellent appearance (transparency, surface lusterand the like) and excellent impact resistance, Unexamined JapanesePatent Application Laid-Open Specification No. 58-141233 discloses acomposition comprising a vinyl aromatic hydrocarbon/1,3-butadiene blockcopolymer and a thermoplastic resin, wherein the block copolymer is amixture of polymer chains which have largely different molecular weightsand different compositions. For improving the environmental stresscracking resistance of a block copolymer, Unexamined Japanese PatentApplication Laid-Open Specification No. 4-277509 (corresponding to U.S.Pat. No. 5,227,419 and European Patent No. 492490) discloses a methodfor producing a block copolymer which comprises a vinyl aromatichydrocarbon and 1,3-butadiene and has gradually varied properties,wherein the method comprises division-wise adding a catalyst to a blockcopolymerization system. For obtaining a multi-layer sheet made of athermoplastic resin (a vinyl aromatic hydrocarbon/isoprene blockcopolymer) which has high stiffness and is improved with respect torapid shaping property at low temperatures and deep draw shapingproperty, Unexamined Japanese Patent Application Laid-Open SpecificationNo. 5-177777 discloses a multi-layer sheet comprising a surface layermade of a first resin having a specific elastic modulus and a layer madeof a second resin, in which the Vicat softening point ratio of the firstresin to the second resin is within a specific range. In an attempt toobtain a block copolymer having excellent transparency and mechanicalproperties, Unexamined Japanese Patent Application Laid-OpenSpecification No. 63-145314 (corresponding to U.S. Pat. No. 4,939,208and European Patent No. 270515) discloses a method for producing a blockcopolymer having an S-B-B/S-S block configuration, wherein each Sindependently represents a styrene polymer block, B represents abutadiene polymer block, and B/S represents a butadiene/styrenecopolymer block. Further, with a view to improving the transparency andimpact resistance of a block copolymer and a composition containing theblock copolymer, Unexamined Japanese Patent Application Laid-OpenSpecification No. 7-97418 discloses a vinyl aromatichydrocarbon/butadiene block copolymer and a composition comprising theblock copolymer, in which the block copolymer has characteristicfeatures with respect to the vinyl aromatic hydrocarbon block ratio, thearrangement of the polymer blocks, the ratio of butadiene in a segmentin which a vinyl aromatic hydrocarbon and butadiene are randomlycopolymerized, and the like.

[0006] However, the conventional block copolymers comprising vinylaromatic hydrocarbon monomer units and conjugated diene monomer unitsdisclosed in the above-mentioned patent documents have a problem in thatthe block copolymers have an unsatisfactory thermal stability and,hence, are susceptible to gelation during the heating thereof at hightemperatures, so that shaped articles (such as a sheet) obtained fromthe block copolymers suffer marked occurrence of FE's which are gelledmasses of a resin. The occurrence of FE's in a shaped article isdisadvantageous, for example, in that, when a print is effected on theshaped article, the print inevitably becomes defective.

SUMMARY OF THE INVENTION

[0007] In this situation, the present inventors have made extensive andintensive studies with a view toward developing a block copolymer whichis advantageous not only in that the block copolymer has excellentthermal stability (that is, even when the block copolymer is heated athigh temperatures, the change in the molecular weight distribution ofthe block copolymer due to crosslinking or breakage of polymer chains ofthe block copolymer can be suppressed), so that occurrence of gelationof the block copolymer during the molding thereof can be suppressed, butalso in that the block copolymer can be advantageously used forproducing a shaped article having excellent stiffness, elongation,impact resistance, transparency and heat shrinkability. As a result, ithas unexpectedly been found that a shaped article, which not only isfree from marked occurrence of FE's, but also has excellent stiffness,elongation, impact resistance, transparency and heat shrinkability, canbe produced by molding a block copolymer comprising at least two Spolymer blocks, each comprising vinyl aromatic hydrocarbon monomerunits, and one B polymer block or two or more B polymer blocks whichcontains or collectively contain isoprene monomer units and1,3-butadiene monomer units, wherein the amount of the vinyl aromatichydrocarbon monomer units, the total amount of the isoprene monomerunits and the 1,3-butadiene monomer units, and the isoprene monomerunit/1,3-butadiene monomer unit weight ratio are within respectivespecific ranges, and wherein the vinyl aromatic hydrocarbon monomer unitmoiety of the block copolymer has a short segment ratio within aspecific range, the short segment ratio being defined as the weightpercentage, based on the total weight of vinyl aromatic hydrocarbonmonomer units contained in the block copolymer, of the vinyl aromatichydrocarbon monomer units contained in at least one short segmentconsisting of 1 to 3 vinyl aromatic hydrocarbon monomer units. Based onthis finding, the present invention has been completed.

[0008] Accordingly, it is a primary object of the present invention toprovide a block copolymer which can be advantageously used for producinga shaped article which not only is free from marked occurrence of FE's,but also has excellent stiffness, elongation, impact resistance,transparency and heat shrinkability.

[0009] The foregoing and other objects, features and advantages of thepresent invention will be apparent from the following detaileddescription and appended claims.

DETAILED DESCRIPTION OF THE INVENTION

[0010] According to the present invention, there is provided a blockcopolymer comprising:

[0011] at least two S polymer blocks, each comprising at least 70% byweight of vinyl aromatic hydrocarbon monomer units, and

[0012] one or more B polymer blocks selected from the following polymerblocks (a), (b) and (c):

[0013] (a) a polymer block comprising isoprene monomer units orcomprising isoprene monomer units and vinyl aromatic hydrocarbon monomerunits,

[0014] (b) a polymer block comprising 1,3-butadiene monomer units orcomprising 1,3-butadiene monomer units and vinyl aromatic hydrocarbonmonomer units, and

[0015] (c) a polymer block comprising isoprene monomer units and1,3-butadiene monomer units or comprising isoprene monomer units,1,3-butadiene monomer units and vinyl aromatic hydrocarbon monomerunits,

[0016] wherein the content of the vinyl aromatic hydrocarbon monomerunits in each of polymer blocks (a) to (c) is less than 70% by weight,

[0017] wherein the one or more B polymer blocks are comprised of onesystem selected from the group consisting of (B-1) to (B-5):

[0018] (B-1) at least one polymer block (a) and at least one polymerblock (b) in combination,

[0019] (B-2) at least one polymer block (a) and at least one polymerblock (c) in combination,

[0020] (B-3) at least one polymer block (a), at least one polymer block(b) and at least one polymer block (c) in combination,

[0021] (B-4) at least one polymer block (b) and at least one polymerblock (c) in combination, and

[0022] (B-5) at least one polymer block (c) alone,

[0023] the amount of the vinyl aromatic hydrocarbon monomer units in theblock copolymer and the total amount of the isoprene monomer units andthe 1,3-butadiene monomer units in the block copolymer being,respectively, from 60 to 95% by weight and from 40 to 5% by weight, eachbased on the weight of the block copolymer,

[0024] the block copolymer having an isoprene monomer unit/1,3-butadienemonomer unit weight ratio of from 45/55 to 97/3, and

[0025] wherein the vinyl aromatic hydrocarbon monomer unit moiety of theblock copolymer has a short segment ratio of from 0 to 30% by weight,wherein the short segment ratio is defined as the weight percentage,based on the total weight of vinyl aromatic hydrocarbon monomer unitscontained in the block copolymer, of the vinyl aromatic hydrocarbonmonomer units contained in at least one short segment consisting of 1 to3 vinyl aromatic hydrocarbon monomer units.

[0026] For easy understanding of the present invention, the essentialfeatures and various preferred embodiments of the present invention areenumerated below.

[0027] 1. A block copolymer comprising:

[0028] at least two S polymer blocks, each comprising at least 70% byweight of vinyl aromatic hydrocarbon monomer units, and

[0029] one or more B polymer blocks selected from the following polymerblocks (a), (b) and (c):

[0030] (a) a polymer block comprising isoprene monomer units orcomprising isoprene monomer units and vinyl aromatic hydrocarbon monomerunits,

[0031] (b) a polymer block comprising 1,3-butadiene monomer units orcomprising 1,3-butadiene monomer units and vinyl aromatic hydrocarbonmonomer units, and

[0032] (c) a polymer block comprising isoprene monomer units and1,3-butadiene monomer units or comprising isoprene monomer units,1,3-butadiene monomer units and vinyl aromatic hydrocarbon monomerunits,

[0033] wherein the content of the vinyl aromatic hydrocarbon monomerunits in each of polymer blocks (a) to (c) is less than 70% by weight,

[0034] wherein the one or more B polymer blocks are comprised of onesystem selected from the group consisting of (B-1) to (B-5):

[0035] (B-1) at least one polymer block (a) and at least one polymerblock (b) in combination,

[0036] (B-2) at least one polymer block (a) and at least one polymerblock (c) in combination,

[0037] (B-3) at least one polymer block (a), at least one polymer block(b) and at least one polymer block (c) in combination,

[0038] (B-4) at least one polymer block (b) and at least one polymerblock (c) in combination, and

[0039] (B-5) at least one polymer block (c) alone,

[0040] the amount of the vinyl aromatic hydrocarbon monomer units in theblock copolymer and the total amount of the isoprene monomer units andthe 1,3-butadiene monomer units in the block copolymer being,respectively, from 60 to 95% by weight and from 40 to 5% by weight, eachbased on the weight of the block copolymer,

[0041] the block copolymer having an isoprene monomer unit/1,3-butadienemonomer unit weight ratio of from 45/55 to 97/3, and

[0042] wherein the vinyl aromatic hydrocarbon monomer unit moiety of theblock copolymer has a short segment ratio of from 0 to 30% by weight,wherein the short segment ratio is defined as the weight percentage,based on the total weight of vinyl aromatic hydrocarbon monomer unitscontained in the block copolymer, of the vinyl aromatic hydrocarbonmonomer units contained in at least one short segment consisting of 1 to3 vinyl aromatic hydrocarbon monomer units.

[0043] 2. The block copolymer according to item 1 above, which comprises(B-5) at least one polymer block (c) alone as the B polymer block.

[0044] 3. The block copolymer according to item 1 above, which comprises(B-1) at least one polymer block (a) and at least one polymer block (b)in combination as the B polymer block.

[0045] 4. The block copolymer according to item 1 above, wherein theisoprene monomer unit/1,3-butadiene monomer unit weight ratio is in therange of from 55/45 to 95/5.

[0046] 5. The block copolymer according to item 1 above, wherein theshort segment ratio is in the range of from 1 to 25% by weight.

[0047] 6. The block copolymer according to item 1 above, which is alinear block copolymer.

[0048] 7. A block copolymer composition comprising 100 parts by weightof the block copolymer of any one of items 1 to 6 above and 0.05 to 3parts by weight of at least one stabilizer which is selected from thegroup consisting of2-(1-(2-hydroxy-3,5-di-t-pentylphenyl)-ethyl)-4,6-di-t-pentylphenylacrylate,2-t-butyl-6-(3-t-butyl-2-hydroxy-5-methylbenzyl)-4-methylphenylacrylate, and 2,4-bis((octylthio)methyl)-o-cresol.

[0049] 8. A block copolymer/styrene resin composition comprising 10 to99% by weight of the block copolymer of any one of items 1 to 6 aboveand 90 to 1% by weight of a styrene resin.

[0050] 9. A block copolymer/styrene resin composition comprising theblock copolymer composition of item 7 above and a styrene resin, whereinthe weight ratio of the block copolymer present in the block copolymercomposition to the styrene resin is 10/90 to 99/1.

[0051] Hereinbelow, the present invention is described in detail.

[0052] In the present invention, the monomer units of the polymer arenamed in accordance with a nomenclature wherein the names of theoriginal monomers from which the monomer units are derived are used withthe term “unit” attached thereto. For example, the term “vinyl aromaticmonomer unit” means a monomer unit which is formed in a polymer obtainedby the polymerization of the vinyl aromatic monomer. The vinyl aromaticmonomer unit has a molecular structure wherein the two carbon atoms of asubstituted ethylene group derived from a substituted vinyl grouprespectively form linkages to adjacent vinyl aromatic monomer units.Similarly, the term “1,3-butadiene monomer unit” means a monomer unitwhich is formed in a polymer obtained by the polymerization of the1,3-butadiene monomer. The 1,3-butadiene monomer unit has a molecularstructure wherein two carbon atoms of an olefin derived from a1,3-butadiene monomer respectively form linkages to adjacent1,3-butadiene monomer units.

[0053] The block copolymer of the present invention comprises:

[0054] at least two S polymer blocks, each comprising at least 70% byweight of vinyl aromatic hydrocarbon monomer units, and

[0055] one or more B polymer blocks selected from the following polymerblocks (a), (b) and (c):

[0056] (a) a polymer block comprising isoprene monomer units orcomprising isoprene monomer units and vinyl aromatic hydrocarbon monomerunits,

[0057] (b) a polymer block comprising 1,3-butadiene monomer units orcomprising 1,3-butadiene monomer units and vinyl aromatic hydrocarbonmonomer units, and

[0058] (c) a polymer block comprising isoprene monomer units and1,3-butadiene monomer units or comprising isoprene monomer units,1,3-butadiene monomer units and vinyl aromatic hydrocarbon monomerunits.

[0059] The above-mentioned one or more B polymer blocks are comprised ofone system selected from the group consisting of (B-1) to (B-5):

[0060] (B-1) at least one polymer block (a) and at least one polymerblock (b) in combination,

[0061] (B-2) at least one polymer block (a) and at least one polymerblock (c) in combination,

[0062] (B-3) at least one polymer block (a), at least one polymer block(b) and at least one polymer block (c) in combination,

[0063] (B-4) at least one polymer block (b) and at least one polymerblock (c) in combination, and

[0064] (B-5) at least one polymer block (c) alone.

[0065] In the present invention, the amount of the vinyl aromatichydrocarbon monomer units in the block copolymer is from 60 to 95% byweight, preferably from 65 to 90% by weight, more preferably from 68 to85% by weight, based on the weight of the block copolymer.

[0066] The total amount of the isoprene monomer units and the1,3-butadiene monomer units in the block copolymer is from 40 to 5% byweight, preferably from 35 to 10% by weight, more preferably from 32 to15% by weight, based on the weight of the block copolymer.

[0067] When the amount of the vinyl aromatic hydrocarbon monomer unitsin the block copolymer is less than 60% by weight, or the total amountof the isoprene monomer units and the 1,3-butadiene monomer units in theblock copolymer is more than 40% by weight, the stiffness of a shapedarticle obtained from the block copolymer is disadvantageously lowered.On the other hand, when the amount of the vinyl aromatic hydrocarbonmonomer units in the block copolymer is more than 95% by weight, and thetotal amount of the isoprene monomer units and the 1,3-butadiene monomerunits in the block copolymer is less than 5% by weight, the elongationand impact resistance of a shaped article obtained from the blockcopolymer are disadvantageously lowered.

[0068] The block copolymer of the present invention has an isoprenemonomer unit/1,3-butadiene monomer unit weight ratio of from 45/55 to97/3, preferably from 50/50 to 97/3, more preferably from 55/45 to 95/5.

[0069] When the isoprene monomer unit/1,3-butadiene monomer unit weightratio is more than 97/3, the block copolymer has the followingdisadvantage. When the block copolymer is heated at high temperatures,the molecular weight distribution of the block copolymer greatly changesdue to breakage of the polymer chains (this means that the amount of lowmolecular weight polymer chains increases). Therefore, the fluidity ofthe block copolymer during the molding thereof becomes disadvantageouslyhigh. On the other hand, when the isoprene monomer unit/1,3-butadienemonomer unit weight ratio is less than 45/55, the block copolymer hasthe following disadvantage. When the block copolymer is heated at hightemperatures, the molecular weight distribution of the block copolymergreatly changes due to the crosslinking of the polymer chains (thismeans that the amount of high molecular weight polymer chainsincreases). Therefore, gelation markedly occurs during the molding ofthe block copolymer.

[0070] In the block copolymer of the present invention, each S polymerblock has a vinyl aromatic hydrocarbon monomer unit content of at least70% by weight, preferably 80% by weight or more, more preferably 90% byweight or more. Each S polymer block may contain monomer units otherthan vinyl aromatic hydrocarbon monomer units. Examples of monomer unitsother than vinyl aromatic hydrocarbon monomer units include a1,3-butadiene monomer unit and an isoprene monomer unit.

[0071] The content of the vinyl aromatic hydrocarbon monomer units ineach of polymer blocks (a), (b) and (c) is less than 70% by weight,preferably 60% by weight or less, more preferably 50% by weight or less.

[0072] With respect to the amount of the isoprene monomer units inpolymer block (a), there is no particular limitation as long as theblock copolymer as a whole has the above-mentioned composition. However,the amount of the isoprene monomer units in polymer block (a) ispreferably 30% by weight or more, more preferably 40% by weight or more,most preferably 50% by weight or more, based on the weight of polymerblock (a).

[0073] With respect to the amount of the 1,3-butadiene monomer units inpolymer block (b), there is no particular limitation as long as theblock copolymer as a whole has the above-mentioned composition. However,the amount of the 1,3-butadiene monomer units in polymer block (b) ispreferably 30% by weight or more, more preferably 40% by weight or more,most preferably 50% by weight or more, based on the weight of polymerblock (b).

[0074] With respect to the total amount of the isoprene monomer unitsand the 1,3-butadiene monomer units in polymer block (c), there is noparticular limitation as long as the block copolymer as a whole has theabove-mentioned composition. However, the total amount of the isoprenemonomer units and the 1,3-butadiene monomer units in polymer block (c)is preferably 30 by weight or more, more preferably 40% by weight ormore, most preferably 50% by weight or more, based on the weight ofpolymer block (c). It is preferred that polymer block (c) is a randomcopolymer.

[0075] Examples of vinyl aromatic monomer units used in S polymer blocksand optionally in B polymer block include a styrene monomer unit, ano-methylstyrene monomer unit, a p-methylstyrene monomer unit, ap-tert-butylstyrene monomer unit, a 2,4-dimethylstyrene monomer unit, ana-methylstyrene monomer unit, a vinyl-naphthalene monomer unit, avinylanthracene monomer unit, and a 1,1-diphenylethylene monomer unit.Of these, a styrene monomer unit is especially preferred. These vinylaromatic monomer units can be used individually or in combination.

[0076] The vinyl aromatic hydrocarbon monomer unit moiety of the blockcopolymer of the present invention has a short segment ratio of from 0to 30% by weight, wherein the short segment ratio is defined as theweight percentage, based on the total weight of vinyl aromatichydrocarbon monomer units contained in the block copolymer, of the vinylaromatic hydrocarbon monomer units contained in at least one shortsegment consisting of 1 to 3 vinyl aromatic hydrocarbon monomer units.The short segment ratio is preferably from 1 to 25% by weight.

[0077] When the short segment ratio is more than 30% by weight, thestiffness of the block copolymer is disadvantageously lowered.

[0078] The short segment ratio can be measured by the following method.The block copolymer is dissolved in dichloromethane. The resultantsolution is subjected to oxidative degradation with ozone (O₃) to obtainan ozonide. The obtained ozonide is subjected to reduction in diethylether in the presence of lithium aluminum hydride, followed byhydrolysis with pure water. From the resultant is recovered a vinylaromatic hydrocarbon component. The vinyl aromatic hydrocarbon componentis subjected to gel permeation chromatography (GPC) to obtain a GPCchromatogram. By calculating the area ratio of the peaks in the obtainedGPC chromatogram, the short segment ratio is obtained (see TakayukiTanaka, Hisaya Sato and Yasunobu Nakafutami, “Koubunshi Gakkai Yokou-shu(Preprints of Meeting of the Society of Polymer Science)”, Vol. 29, p.2051, 1980, Japan).

[0079] The short segment ratio can be controlled by appropriatelyadjusting the amounts of vinyl aromatic hydrocarbon monomers, isoprenemonomers and 1,3-butadiene monomers which are subjected tocopolymerization, the relationship between polymerization reactivitiesof the monomers subjected to copolymerization and the like.Illustratively stated, the short segment ratio can be controlled by amethod in which vinyl aromatic hydrocarbon monomers, isoprene monomersand 1,3-butadiene monomers are copolymerized while continuously adding amixture thereof to the polymerization reaction system, or by a method inwhich vinyl aromatic hydrocarbon monomers, isoprene monomers and1,3-butadiene monomers are subjected to copolymerization in the presenceof a polar compound or a randomizing agent. These methods can beemployed individually or in combination.

[0080] Examples of polar compounds and randomizing agents includeethers, such as tetrahydrofuran, diethylene glycol dimethyl ether anddiethylene glycol dibutyl ether; amines, such as triethylamine andtetramethylethylenediamine; thioethers; phosphines; phosphoramides;alkylbenzenesulfonates; and potassium and sodium alkoxides.

[0081] As examples of block copolymers of the present invention, therecan be mentioned linear block copolymers having block configurationsrepresented by the following formulae (1), (2) and (3):

S—(B—S)_(n)  (1),

S—(B—S)_(n)—B  (2)

and

S—(S—B)_(n+1)  (3).

[0082] As further examples of block copolymers of the present invention,there can be mentioned radial block copolymers having blockconfigurations represented by the following formulae (4), (5), (6) and(7):

((S—B)_(k))_(m+2)—X  (4),

((S—B)_(k)—S)_(m+2)—X  (5),

((B—S)_(k))_(m+2)—X  (6)

and

((B—S)_(k)—B)_(m+2)—X  (7).

[0083] In formulae (1) to (7) above, each S independently represents anS polymer block, which has a vinyl aromatic hydrocarbon monomer unitcontent of at least 70% by weight.

[0084] In formulae (1) to (7) above, each B independently represents a Bpolymer block. When the above-mentioned one or more B polymer blocks arecomprised of any one of the above-mentioned systems (B-1), (B-2), (B-3)and (B-4), the block copolymer of any of formulae (1) to (7) above hastwo or more different B blocks. As a specific example of blockcopolymers of formula (1) above, there can be mentioned a blockcopolymer in which the above-mentioned one or more B polymer blocks arecomprised of system (B-1), and n is 2, which is a block copolymerrepresented by the following formula:

S—B(a)—S—B(b)—S

[0085] wherein each S independently represents an S polymer block, B(a)represents the above-mentioned polymer block (a), and B(b) representsthe above-mentioned polymer block (b).

[0086] In formulae (4) to (7) above, X represents a residue of acoupling reagent, such as silicon tetrachloride, tin tetrachloride,epoxidized soybean oil, tetraglycidyl-1,3-bisaminomethylcyclohexane, ahydrocarbon polyhalide, a carboxylic ester or a polyvinyl compound; or aresidue of a polymerization initiator, such as a multifunctionalorganolithium compound.

[0087] In formulae (1) to (7) above, each of n, k and m represents anatural number. Each of n, k and m is generally from 1 to 5.

[0088] The block copolymer of the present invention can be produced byconventional methods. For example, the block copolymer can be producedby a method in which a vinyl aromatic hydrocarbon, isoprene and1,3-butadiene are polymerized in an organic solvent in the presence ofan organolithium compound as a polymerization initiator.

[0089] As an example of organic solvents used for producing the blockcopolymer, there can be mentioned a hydrocarbon solvent. Examples ofhydrocarbon solvents include aliphatic hydrocarbons, such as butane,pentane, hexane, isopentane, heptane, octane and isooctane; alicyclichydrocarbons, such as cyclopentane, methylcyclopentane, cyclohexane,methylcyclohexane and ethylcyclohexane; and aromatic hydrocarbons, suchas benzene, toluene, ethylbenzene and xylene. These hydrocarbon solventscan be used individually or in combination.

[0090] The organolithium compound, which is used as a polymerizationinitiator for producing the block copolymer, is an organic compoundhaving in a molecule thereof at least one lithium atom. That is, theorganolithium compound can be any of an organomonolithium compound, anorganodilithium compound and an organopolylithium compound. Examples oforganolithium compounds include ethyllithium, n-propyllithium,isopropyllithium, n-butyllithium, sec-butyllithium, tert-butyllithium,hexamethylenedilithium, butadienyldilithium and isoprenyldilithium.These organolithium compounds can be used individually or incombination.

[0091] When the block copolymer of the present invention is produced bythe above-mentioned method, the polymerization reaction conditions areas follows. The polymerization reaction temperature is generally from−10 to 150° C., preferably from 40 to 120° C. The polymerizationreaction time varies depending on other reaction conditions; however,the polymerization reaction time is generally 10 hours or less, mostpreferably from 0.5 to 5 hours. It is preferred that the polymerizationis performed in the atmosphere of an inert gas, such as nitrogen gas.With respect to the polymerization reaction pressure, there is noparticular limitation as long as the pressure is sufficient to maintainthe monomers and the solvent in a liquid state at a temperature withinthe above-mentioned polymerization reaction temperature range. Further,care must be taken so as to prevent impurities (such as water, oxygenand carbon dioxide gas), which are likely to deactivate not only thepolymerization catalyst but also a living polymer being formed, fromintruding into the polymerization reaction system.

[0092] From the viewpoint of the improvement in processability of theblock copolymer, the melt flow rate (hereinafter, frequently referred toas “MFR”) of the block copolymer is generally from 0.1 to 50 g/10 min,preferably from 1 to 20 g/10 min. In the present invention, MFR ismeasured in accordance with JISK-6870 under condition G (temperature:200° C., load: 5 kg).

[0093] The block copolymer of the present invention exhibits excellentthermal stability even when heated at high temperatures. Enhancement ofthe thermal stability of the block copolymer can be achieved by addingthereto at least one stabilizer to thereby obtain the block copolymercomposition of the present invention, wherein the stabilizer is selectedfrom the group consisting of2-(1-(2-hydroxy-3,5-di-t-pentylphenyl)ethyl)-4,6-di-t-pentylphenylacrylate,2-t-butyl-6-(3-t-butyl-2-hydroxy-5-methylbenzyl)-4-methylphenylacrylate, and 2,4-bis((octylthio)methyl)-o-cresol. The amount of thestabilizer is from 0.05 to 3 parts by weight, preferably from 0.1 to 2parts by weight, relative to 100 parts by weight of the block copolymer.

[0094] When the amount of the stabilizer is less than 0.05 part byweight, it becomes difficult to satisfactorily suppress the change inthe molecular weight distribution of the block copolymer in thecomposition, which occurs due to the crosslinking or breakage of polymerchains of the block copolymer when the block copolymer composition isheated at high temperatures. On the other hand, even when the stabilizeris added to the block copolymer in an amount of more than 3 parts byweight, the effect of suppressing the change in the molecular weightdistribution of the block copolymer does not increase, as compared tothe case where the stabilizer is added to the block copolymer in anamount of from 0.05 to 3 parts by weight.

[0095] The block copolymer of the present invention and the blockcopolymer composition of the present invention can be used for producinga shaped article having excellent stiffness, elongation, impactresistance and transparency. Such an excellent effect of the blockcopolymer and the block copolymer composition can be enhanced by addinga styrene resin thereto to obtain a block copolymer/styrene resincomposition.

[0096] The amounts of the block copolymer and the styrene resin in theblock copolymer/styrene resin composition are, respectively, from 10 to99% by weight and from 90 to 1% by weight, preferably from 10 to 90% byweight and from 90 to 10% by weight, more preferably from 15 to 85% byweight and from 85 to 15% by weight, based on the total weight of theblock copolymer and the styrene resin.

[0097] When the amounts of the block copolymer and the styrene resinare, respectively, less than 10% by weight and more than 90% by weight,the impact resistance of a shaped article obtained from the blockcopolymer/styrene resin composition is disadvantageously lowered. On theother hand, when the amounts of the block copolymer and the styreneresin are, respectively, more than 99% by weight and less than 1% byweight, the surface properties (smoothness, blocking resistance and thelike) and stiffness of a shaped article obtained from the blockcopolymer/styrene resin composition cannot be satisfactorily improved.

[0098] As the styrene resin, a non-rubber-modified styrene polymer canbe used. A rubber-modified polystyrene can also be used as long as theblock copolymer/styrene resin composition retains transparency.

[0099] Examples of non-rubber-modified styrene polymers include apolymer comprising at least one styrene type monomer selected fromstyrene, an α-alkyl-substituted styrene (e.g., α-methylstyrene), analkyl substituted styrene having a structure in which an aromaticnucleus of styrene is substituted with an alkyl group, and anhalogen-substituted styrene having a structure in which an aromaticnucleus of styrene is substituted with a halogen atom. Further examplesof non-rubber-modified styrene polymers include a copolymer of at leastone styrene type monomer selected from the above-mentioned styrene typemonomers with at least one monomer which is copolymerizable with thestyrene type monomer, wherein the amount of styrene type monomer is 50%by weight or more, preferably 70% by weight or more, based on the weightof the copolymer.

[0100] Examples of monomers which is copolymerizable with the styrenetype monomer include acrylic acid and esters thereof, such as an alkylacrylate wherein the alkyl group has 1 to 12 carbon atoms (e.g., methylacrylate, ethyl acrylate, propyl acrylate and butyl acrylate);methacrylic acid and esters thereof, such as an alkyl methacrylatewherein the alkyl group has 1 to 12 carbon atoms (e.g., methylmethacrylate, ethyl methacrylate and butyl methacrylate);α,β-unsaturated dicarboxylic acids, such as fumaric acid, maleic acidand itaconic acid, and monoesters, diesters, anhydrides and imidethereof (e.g., maleic anhydride and maleimide).

[0101] Preferred examples of styrene resins include a polystyrene, astyrene/n-butyl acrylate copolymer and a styrene/methyl methacrylatecopolymer. These polymers can be used individually or in combination.

[0102] The block copolymer/styrene resin composition of the presentinvention can be produced by any conventional method. Examples of suchconventional methods include a melt-kneading method using a mixergenerally used in the art, such as an open roll, an intensive mixer, aninternal mixer, Ko-kneader, a continuous kneader having a twin-rotor, oran extruder, and a method in which each component is dissolved ordispersed in a solvent, followed by removal of the solvent by heating.

[0103] Each of the block copolymer, block copolymer composition andblock copolymer/styrene resin composition of the present invention mayfurther contain at least one phenolic stabilizer, such asn-octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate,tetrakis(methylene-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate)methane,1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene, and2,4-bis(n-octylthio)-6-(4-hydroxy-3,5-di-t-butylanilino)-1,3,5-triazine.The amount of the phenolic stabilizer is generally from 0.05 to 3 partsby weight, relative to 100 parts by weight of the block copolymer.

[0104] Each of the block copolymer, block copolymer composition andblock copolymer/styrene resin composition of the present invention mayfurther contain at least one organic phosphate or phosphite stabilizer,such as tris(nonylphenyl)phosphite,2,2-methylenebis(4,6-di-t-butylphenyl)octylphosphite,2-((2,4,8,10-tetrakis(1,1-dimethylethyl)dibenzo(d,f)(1,3,2)dioxaphosphepin-6-yl)oxy)-N,N-bis(2-((2,4,8,10-tetrakis(1,1-dimethylethyl)dibenzo(d,f)(1,3,2)dioxaphosphepin-6-yl)oxy)ethyl)ethaneamine,and tris(2,4-di-t-butylphenyl)phosphite. The amount of the organicphosphate or phosphite stabilizer is generally from 0.05 to 3 parts byweight, relative to 100 parts by weight of the block copolymer.

[0105] If desired, an additive can be added to the block copolymer,block copolymer composition and block copolymer/styrene resincomposition of the present invention. Examples of additives includepolymeric additives, such as a vinyl aromatic hydrocarbon/conjugateddiene block copolymer elastomer in which the vinyl aromatic hydrocarbonmonomer unit content is 50% by weight or less, and polyethyleneterephthalate.

[0106] Further examples of additives include those which have beenconventionally used as additives for plastics. Examples of suchadditives include inorganic reinforcing agents, such as glass fiber,glass bead, silica, calcium carbonate and talc; organic reinforcingagents, such as organic fiber, a coumarone-indene resin; crosslinkingagents, such as an organic peroxide and an inorganic peroxide; pigments,such as titanium white, carbon black and iron oxide; dyes; flameretardants; antioxidants; ultraviolet light absorbers; antistaticagents; lubricants; plasticizers; fillers other than mentioned above;and mixtures thereof.

[0107] Each of the block copolymer, block copolymer composition andblock copolymer/styrene resin composition of the present invention perse or a mixture thereof with a coloring agent can be molded by the samemolding method as employed in the molding of an ordinary thermoplasticresin to obtain shaped articles for use in various application fields.For example, the molding can be conducted by injection molding or blowmolding to obtain a container for parts of office automationapparatuses, daily commodities, food, miscellaneous goods, parts oflight electric appliances and the like. Especially, each of the blockcopolymer, block copolymer composition and block copolymer/styrene resincomposition of the present invention can be advantageously used forproducing a thin film (such as a heat shrinkable film or a laminatefilm) and a transparent sheet (such as a blister case for food or partsof light electric appliances).

BEST MODE FOR CARRYING OUT THE INVENTION

[0108] Hereinbelow, the present invention will be described in moredetail with reference to the following Examples and ComparativeExamples, which should not be construed as limiting the scope of thepresent invention.

[0109] Various properties of block copolymers used in the followingExamples and Comparative Examples were measured as follows.

[0110] (1) Melt Flow Rate (MFR):

[0111] MFR is measured in accordance with JISK-6870 under condition Gprescribed therein (temperature: 200° C., load: 5 kg).

[0112] (2) Short Segment Ratio:

[0113] An ozone (O₃)-containing oxygen gas having an ozone content of1.5% is introduced into a solution of a block copolymer indichloromethane at a rate of 150 ml/min to conduct an oxidativedegradation of the block copolymer, thereby obtaining an ozonide. Theobtained ozonide is dropwise added to a mixture of diethyl ether withlithium aluminum hydride, to thereby effect a reduction of the ozonide.Then, to, the resultant is dropwise added pure water to effecthydrolysis of the reduced product, followed by addition of potassiumcarbonate to salt out a vinyl aromatic hydrocarbon component. Theresultant precipitated vinyl aromatic hydrocarbon component is recoveredby filtration. The recovered vinyl aromatic hydrocarbon component issubjected to gel permeation chromatography (GPC) to obtain a GPCchromatogram. By calculating the area ratio of the peaks in the obtainedGPC chromatogram, the short segment ratio is obtained (see TakayukiTanaka, Hisaya Sato and Yasunobu Nakafutami, “Koubunshi Gakkai Yokoushu(Preprints of Meeting of the Society of Polymer Science)”, Vol. 29, p.2051, 1980, Japan). In the above-mentioned oxidative degradation, as anapparatus for generating ozone, an ozone generating machine (OT-31R-2,manufactured and sold by Nippon Ozone Co., Ltd., Japan) is used. In theGPC, chloroform is used as a solvent. The GPC is conducted usingshimpack HSG-40H, shimpack GPC-802 and shimpack GPC-801 (each of whichis manufactured and sold by Shimadzu Corporation, Japan) which areconnected in series in this order as viewed in the direction of flow ofthe solvent.

[0114] Further, in the following Examples and Comparative Examples, thefollowing evaluations were made.

[0115] (1) Thermal Stability:

[0116] With respect to each of stabilizer-containing block copolymercompositions which have the compositions shown in Table 3 or 4 exceptthat styrene resins shown in Table 3 or 4 are not used, the thermalstability is evaluated as follows. The block copolymer composition isheated to 230° C. in a nitrogen gas atmosphere and, then, allowed tostand still for 60 minutes. Before the heating and after 60 minutes ofthe standing, the block copolymer is subjected to GPC, thereby obtainingtwo GPC charts (hereinafter, the GPC charts obtained with respect to theblock copolymer before the t heating and after 60 minutes of thestanding are referred to as “first GPC chart” and “second GPC chart”,respectively). The first and second GPC charts, which have the same sizeand the same peak area, are superimposed. Since the molecular weightdistribution of the block copolymer is broadened by the heating thereof,the peak in the second GPC chart is broader than that in the first GPCchart. Therefore, the superimposed GPC charts contains non-overlappingpeak portions which are positioned at both sides (i.e., a high molecularweight side and a low molecular weight side) of the peak of the firstGPC chart.

[0117] The ratio of the area of the non-overlapping portion of the peakon the low molecular weight side to the area of the whole peak isdefined as the low molecular weight component ratio (% by weight),whereas the ratio of the area of the non-overlapping portion of the peakon the high molecular weight side to the area of the whole peak isdefined as the high molecular weight component ratio (% by weight).

[0118] The increase in the low molecular weight component ratio meansthe increase in the occurrence of the breakage of polymer chains of theblock copolymer. The increase in the high molecular weight componentratio means the increase in the occurrence of the crosslinking ofpolymer chains of the block copolymer.

[0119] (2) Surface Impact Strength (Index for Impact Resistance):

[0120] The measurement is conducted at 23° C. in accordance withASTMD-1709, except that the diameter of the weight is ½ inch, to obtaina 50% breakage value.

[0121] (3) Modulus in Tension (Index for Stiffness) and Elongation atBreak:

[0122] With respect to a test sample in the form of a sheet having awidth of 12.7 mm, the measurement is conducted at a pulling rate of 5mm/min with respect to each of an extrusion direction of the sample anda direction perpendicular to the extrusion direction, wherein thedistance between the gage marks is 50 mm.

[0123] (4) Haze:

[0124] The surface of a sheet is coated with liquid paraffin and, then,the haze of the sheet is measured in accordance with ASTM D1003.

[0125] (5) Fish Eye (FE):

[0126] Sheets having a thickness of 0.3 mm are continuously produced for6 hours by continuously molding a block copolymer composition or a blockcopolymer/styrene resin composition at an extrusion temperature of 235°C. using a 40 mm sheet extruder (i.e., an extruder for producing sheets,which has a screw having a diameter of 40 mm). With respect to each ofthe sheets produced at the points in time of 5 minutes and 6 hours afterthe start of the continuous molding, the number of FE's having a size of0.5 mm or more observed per 300 cm² of the sheet is counted. Based onthe difference in the number of FE's between the two sheets, theoccurrence of FE's is evaluated as follows:

[0127] ◯: The difference is less than 50.

[0128] Δ: The difference is from 50 to 100.

[0129] X: The difference is more than 100.

[0130] (6) 80° C. Shrinkage Factor (Index for Shrinkability at LowTemperatures):

[0131] A heat shrinkable film having a thickness of about 60 μm isimmersed in hot water having a temperature of 80° C. for 5 minutes,wherein, as described below in Examples 16 and 17, the heat shrinkablefilm is obtained by uniaxially stretching a 0.25 mm-thick sheet made ofa block copolymer/styrene resin composition 5-fold at 104° C. in adirection perpendicular to an extrusion direction of the sheet by theuse of a tenter. The 80° C. shrinkage factor of the heat shrinkable filmis calculated by the following formula:

80° C. shrinkage factor (%)={(L−L ₁)/L}×100

[0132] wherein L represents the length of the heat shrinkable filmbefore the immersion thereof in the hot water having a temperature of80° C., and L₁ represents the length of the heat shrinkable film after 5minutes of the immersion thereof in the hot water.

[0133] (7) Natural Shrinkage Factor:

[0134] With respect to each of three heat shrinkable films having athickness of about 60 μm, the 80° C. shrinkage factor thereof ismeasured in accordance with the above-mentioned method, wherein, asdescribed below in Examples 16 and 17, these three heat shrinkable filmsare, respectively, obtained by uniaxially stretching 0.25 mm-thicksheets made of a block copolymer/styrene resin composition 5-fold at104° C., 108° C. and 112° C. in a direction perpendicular to anextrusion direction of the sheet by the use of a tenter. Each of thethree heat shrinkable films is allowed to stand still at 35° C. for 5days and, then, the “NS value” which is defined by the following formulais obtained:

NS value (%)={(L ₂ −L ₃)/L ₂}×100

[0135]  wherein L₂ and L₃ represent the lengths of the sheet before andafter 5 days of the standing at 35° C., respectively.

[0136] The obtained three NS values (ordinate) are plotted against the80° C. shrinkage factor values (abscissa) to obtain a graph showing arelationship between the 80° C. shrinkage factor and the NS value. Fromthe obtained graph, the NS value at a 80° C. shrinkage factor of 40% isobtained. The thus obtained NS value (at a 80° C. shrinkage factor of40%) is defined as the natural shrinkage factor.

[0137] (8) Resistance to Fusion Bonding in Hot Water:

[0138] Each of three heat shrinkable films (which are the same as usedin item (6) above) is twined around a glass bottle having a diameter ofabout 8 cm. Then, the three glass bottles are immersed in hot waterhaving a temperature 70° C. and allowed to stand still in the hot waterfor 5 minutes, wherein the three glass bottles are placed in the hotwater so that the three glass bottles are in contact with each otherthrough the heat shrinkable films. Then, the conditions of the filmstwined round the glass bottles are visually observed, and the resistanceto fusion bonding in hot water is evaluated in accordance with thefollowing criteria:

[0139] ⊚: The films are not fusion bonded to each other at all.

[0140] ◯: The films are fusion bonded to each other so weakly that thefilms are easily separated from each other.

[0141] X: The films are fusion bonded to each other so strongly thatfilms are not easily separated from each other.

[0142] Styrene resins A-1 to A-3, which were used in the followingExamples and Comparative Examples, are shown in Table 1 below.

[0143] Styrene resin A-1 is a general-purpose polystyrene (manufacturedand sold by A & M Styrene Co., Ltd., Japan). The MFR of styrene resinA-1 was measured and found to be 2.8.

[0144] Styrene resin A-2 (styrene/n-butyl acrylate copolymer) wasproduced as follows.

[0145] To a 10-liter autoclave equipped with a stirrer were added 4.2 kgof styrene and 0.8 kg of n-butyl acrylate simultaneously with 0.3 kg ofethylbenzene and 1 g of 1,1-bis(t-butylperoxy)cyclohexane (which wasused for adjusting the MFR of styrene resin A-2 to be produced). Then,polymerization reaction was performed, while changing the reactiontemperature as follows: at 110° C. for 3 hours, at 130° C. for 3 hours,and at 150° C. for 2 hours. The polymerization pressure was 1.5 kg/cm²G.From the resultant polymer were removed unreacted monomers (i.e.,styrene, n-butyl acrylate, and ethylbenzene) using a vented extruder tothereby obtain styrene resin A-2. The MFR of styrene resin A-2 wasmeasured and found to be 3.0.

[0146] Styrene resin A-3 (styrene/n-butyl acrylate copolymer) wasproduced in substantially the same manner as in the production ofstyrene resin A-2, except that the composition of the copolymer waschanged as shown in Table 1. The MFR of styrene resin A-3 was measuredand found to be 3.0.

[0147] Each of Block copolymers B-1 to B-17 used in the followingExamples and Comparative Examples was produced as follows.Polymerization was performed in a cyclohexane solvent in the presence ofn-butyllithium as a polymerization initiator, wherein monomers are addedto a polymerization reaction system in amounts wherein the compositiondescribed in the item “block configuration” of Table 2 is achieved andin an order wherein a block copolymer having a block configurationdescribed in Table 2 is formed from the left end to the right end of theblock configuration, to thereby obtain a block copolymer. To theobtained block copolymer were added stabilizers to obtain a blockcopolymer in the form of a composition thereof with stabilizers.

[0148] The types and amounts of stabilizers added to block copolymersB-1 to B-16 are described in Tables 3 and 4. The types and amounts ofstabilizers added to block copolymer B-17 are described in Table 5.

[0149] With respect to the method for producing block copolymer B-1, amore detailed explanation is made below. Into a 30-liter sealed reactorhaving a jacket were charged a 20% by weight cyclohexane solution of amixture of isoprene and 1,3-butadiene, which contains 6 parts by weightof isoprene and 2 parts by weight of 1,3-butadiene. Into the reactorwere charged 0.085 part by weight of n-butyllithium. The reactor waspurged with nitrogen gas. A first polymerization reaction was performedat 80° C. for 20 minutes while maintaining the pressure in the reactorwithin the range of from 3 to 5 kg/cm²G. Then, a 20% by weight solutionof styrene in cyclohexane, which contains 21 parts by weight of styrene,was charged at one time into the reactor to perform a secondpolymerization reaction at 80° C. for 20 minutes. Then, a 20% by weightcyclohexane solution of a mixture of isoprene and 1,3-butadiene, whichcontains 3 parts by weight of isoprene and 1 part by weight of1,3-butadiene, was charged at one time into the reactor to perform athird polymerization reaction at 80° C. for 10 minutes. Then, a fourthpolymerization reaction was performed at 80° C. while continuouslycharging over 30 minutes into the reactor a 20% by weight cyclohexanesolution of a mixture of isoprene, 1,3-butadiene and styrene, whichcontains 11 parts by weight of isoprene, 7 parts by weight of1,3-butadiene and 5 parts by weight of styrene. Then, a 20% by weightsolution of styrene in cyclohexane, which contains 44 parts by weight ofstyrene, was charged at one time into the reactor to perform a fifthpolymerization reaction at 80° C. for 35 minutes. Thereafter, methanolwas fed to the reactor in a molar amount 0.9 time the molar amount ofthe n-butyllithium used, and the contents of the reactor were stirredfor 5 minutes. followed by addition of stabilizers. Then, thecyclohexane solvent was removed from the reactor. Thus, block copolymerB-1 was obtained in the form of a composition thereof with stabilizers.

[0150] With respect to block copolymers B-2 to B-4, B-6 to B-10 and B-12to B-17, the production thereof were performed in substantially the samemanner as in the production of block copolymer B-1, except that thetypes and amounts of components used were changed as described in Tables2 to 5. With respect to block copolymers B-5 and B-11, the productionthereof were performed in substantially the same manner as in theproduction of block copolymer B-1, except that types and amounts ofcomponents used were changed as described in Tables 2 to 4, and that,before the charging of methanol into the reactor, silicon tetrachloridewas charged into the reactor in a molar amount 0.25 time the molaramount of the n-butyllithium used.

[0151] All of the MFR's of block copolymers B-1 to B-17 were measuredand found to be in the range of from 5 to 10, wherein the measurement ofthe MFR of each of block copolymers B-1 to B-17 was conducted withrespect to the composition thereof with stabilizers.

[0152] The styrene content (% by weight), short segment ratio (% byweight) and block configuration of each of block copolymers B-1 to B-17are shown in Table 2.

[0153] The measurement of the short segment ratio of each of blockcopolymers B-1 to B-17 was conducted with respect to a sample of theblock copolymer, which was taken before the addition of the stabilizers.

EXAMPLES 1 TO 15 AND COMPARATIVE EXAMPLES 1 to 4

[0154] In each of Examples 1 to 15 and Comparative Examples 1 to 4, ablock copolymer composition or block copolymer/styrene resin compositionhaving a composition shown in Table 3 or 4 was subjected to extrusionmolding at an extrusion temperature of 200° C. using a 40 mm sheetextruder, thereby obtaining a sheet having a thickness of 0.25 mm. Themodulus in tension, elongation at break and haze of the sheet weremeasured in accordance with the above-mentioned methods. Further, asheet having a thickness of 0.6 mm was produced by substantially thesame method as described above, and the surface impact strength of thesheet was measured in accordance with the above-mentioned method. Also,FE was evaluated in accordance with the above-mentioned method.

[0155] The results are shown in Tables 3 and 4.

EXAMPLES 16 AND 17

[0156] In each of Examples 16 and 17, a block copolymer/styrene resincomposition having a composition shown in Table 5 was subjected toextrusion molding at an extrusion temperature of 200° C. using a 40 mmsheet extruder, thereby obtaining a sheet having a thickness of 0.25 mm.

[0157] Using a tenter, a sample of the obtained sheet was uniaxiallystretched 5-fold at 104° C. in a direction perpendicular to an extrusiondirection of the sheet to obtain a stretched film (a heat shrinkablefilm) having a thickness of about 60 μm. With respect to the obtainedstretched film, the 80° C. shrinkage factor and the resistance to fusionbonding in hot water were measured in accordance with theabove-mentioned methods.

[0158] In addition, using the tenter, further samples of the sheethaving a thickness of 0.25 mm were stretched 5-fold at 108° C. and at112° C., respectively, in a direction perpendicular to an extrusiondirection of the sheet to obtain two stretched films (heat shrinkablefilms), each having a thickness of about 60 μm.

[0159] With respect to the thus obtained three stretched films, eachhaving a thickness of about 60 μm, the natural shrinkage factor thereofwas measured in accordance with the above-mentioned method.

[0160] The results are shown in Table 5. TABLE 1 A-1 A & M polystyrene685 A-2 Styrene/n-butyl acrylate copolymer (styrene content: 84% byweight) A-3 Styrene/n-butyl acrylate copolymer (styrene content: 78% byweight)

[0161] TABLE 2 Styrene Short seg- content Isoprene/1,3- ment ratio (% bybutadiene (% by weight) weight ratio weight) Block configuration *1 B-170 67/33 3.8 I/B(6/2)-S₁(21)-I/B(3/1)-I/B/S(11/7/5)-S₂(44) B-2 82 56/449.5 S₁(38)-I/B/S(10/8/13)-S₂(31) B-3 76 71/29 17.6S₁(32)-I/B(9/1)-I/B/S(8/6/18)-S₂(26) B-4 68 81/19 9.1S₁(15)-I/B(11/1)-I/B/S(15/5/9)-S₂(44) B-5 73 63/37 10.8[S₁(45)-I/B/S(15/9/13)-S₂(15)-I/B(2/1)]₄X B-6 77 48/52 7.8S₁(33)-I/B/S(11/12/9)-S₂(35) B-7 72 86/14 4.2I(6)-S₁(23)-B(4)-I/S(18/5)-S₂(44) B-8 80 60/40 8.9S₁(34)-I/S(12/8)-B/S(8/5)-S₂(33) B-9 77 61/39 10.1S₁(30)-I(5)-B(5)-B/S(4/8)-I/S(9/10)-S₂(29) B-10 70 80/20 7.1S₁(16)-I(9)-B(2)-I/S(15/7)-B/S(4/2)-S₂(45) B-11 72 71/29 8.3[S₁(46)-I/S(15/8)-B/S(8/4)-S₂(14)-I(5)]₄X B-12 75 56/44 13.1S₁(24)-I/S(14/10)-B/S(11/8)-S₂(33) B-13 57 23/77 0.9I/B(5/15)-S₁(10)-I/B/S(5/18/2)-S₂(45) B-14 96 75/25 4.2S₁(43)-I/B/S(3/1/6)-S₂(47) B-15 70 17/83 31.2S₁(15)-I(5)-B/S(25/37)-S₂(18) B-16 75 28/72 10.6S₁(20)-I/B(3.5/5.5)-I/B/S(3.5/5.5/15)-B(7)-S₂(40) B-17 73 78/22 28.9I/B/S(3/1/32)-I/B/S(15/4/22)-I/B/S(3/1/19) #independently represents a1,3-butadiene/styrene copolymer block, each “I/B” independentlyrepresents an isoprene/1,3-butadiene copolymer block, each “I/B/S”independently represents an isoprene/1,3-butadiene/styrene copolymerblock, #each of “S”, “S₁” and “S₂” independently represents a styrenepolymer block, and “X” represents a silicon tetrachloride residue.Numbers shown in parentheses indicate the amounts of components (% byweight).

[0162] TABLE 3 Example 1 Example 2 Example 3 Example 4 Example 5 Example6 Example 7 Example 8 Composition Type and amount of the styrene resinA-2 A-1 A-2 A-2 A-2 A-1 A-1/A-2 — (% by weight) *1 45 25 50 10/50 50 205/45 Type and amount of the block copolymer B-1 B-2 B-3 B-4 B-5 B-6 B-1B-2 (% by weight) *1 55 75 50 40 50 80 50 100 Stabilizer Type of thestabilizer *2 A/D A/B/C A/C/F A/D/E A/B/F D/F A/D A/B/C Amount of thestabilizer *3 A: 0.3 A: 0.1 A: 0.1 A: 1.2 A: 0.5 D: 0.2 A: 0.2 A: 0.1(part by weight) D: 0.1 B: 0.2 C: 0.1 D: 0.5 B: 0.2 F: 0.4 D: 0.1 B: 0.2C: 0.1 F: 0.3 E: 0.1 F: 0.3 C: 0.1 Thermal stability High molecularweight component ratio 0.6 1.0 0.6 0.5 0.6 1.8 0.6 1.0 (% by weight) Lowmolecular weight component ratio 0.7 0.5 0.9 0.3 0.5 1.0 0.7 0.5 (% byweight) Properties of the sheet Modulus in tension extrusion direction12500 14600 13400 13200 13800 13700 13100 13600 (kgf/cm²) directionperpendicular 11000 13300 11600 12400 12900 13400 11300 12700 to theextrusion direction Elongation at break (%) extrusion direction 90 35 7075 50 60 70 85 direction perpendicular 135 55 100 85 95 70 125 105 tothe extrusion direction Surface impact strength (kg · cm) 100 70 80 8060 65 85 90 Haze (%) 0.7 1.3 0.7 0.8 0.7 1.4 1.0 0.5 FE 603 603 603 603603 Δ 603 603

[0163] TABLE 4 Example Example Example Example Example Example 9 10 1112 13 14 Composition Type and amount of the styrene resin A-2 A-1 A-2A-2 A-2 A-1/A-2 (% by weight) *1 45 20 55 60 55 10/10 Type and amount ofthe block copolymer B-7 B-8 B-9 B-10 B-11 B-12 (% by weight) *1 55 80 4540 45 80 Stabilizer Type of the stabilizer *2 A/D/E A/B/F A/D A/D/FA/B/C A/D/F Amount of the stabilizer *3 A: 0.2 A: 0.5 A: 0.3 A: 1.2 A:0.2 A: 0.5 (part by weight) D: 0.1 B: 0.2 D: 0.1 D: 0.3 B: 0.2 D: 0.2 E:0.1 F: 0.3 F: 0.5 C: 0.1 F: 0.4 Thermal stability High molecular weightcomponent ratio 0.6 0.8 0.7 0.5 0.7 0.9 (% by weight) Low molecularweight component ratio 0.9 0.3 0.9 0.4 0.6 0.9 (% by weight) Propertiesof the sheet Modulus in tension extrusion direction 12800 14200 1390013500 14100 13400 (kgf/cm²) direction perpendicular 11100 12900 1200012400 13300 13100 to the extrusion direction Elongation at break (%)extrusion direction 80 40 60 70 45 65 direction perpendicular 135 60 8580 80 75 to the extrusion direction Surface impact strength (kg · cm) 9575 70 80 55 70 Haze (%) 0.7 1.2 0.6 0.8 0.7 1.0 FE 603 603 603 603 603603 Example Comparative Comparative Comparative Comparative 15 Example 1Example 2 Example 3 Example 4 Composition Type and amount of the styreneresin — A-1/A-2 A-1 A-2 A-1/A-2 (% by weight) *1 10/40 95 45 30/30 Typeand amount of the block copolymer B-12 B-15 B-14 B-13 B-16 (% by weight)*1 100 50 5 55 40 Stabilizer Type of the stabilizer *2 A/D/F E/F E/D A/FF Amount of the stabilizer *3 A: 0.5 E: 0.1 E: 0.3 A: 0.2 F: 0.5 (partby weight) D: 0.2 F: 0.2 D: 0.1 F: 0.1 F: 0.4 Thermal stability Highmolecular weight component ratio 0.9 6.8 0.8 4.8 3.2 (% by weight) Lowmolecular weight component ratio 0.9 1.3 3.2 1.0 2.9 (% by weight)Properties of the sheet Modulus in tension extrusion direction 120008400 27000 10500 15500 (kgf/cm²) direction perpendicular 10500 500026000 7400 13400 to the extrusion direction Elongation at break (%)extrusion direction 110 150 or more 3 or less 150 or more 45 directionperpendicular 155 150 or more 3 or less 150 or more 60 to the extrusiondirection Surface impact strength (kg · cm) 140 200 or more 3 or less200 or more 45 Haze (%) 0.5 1.6 0.5 3.9 1.8 FE 603 X 603 X Δ

[0164] TABLE 5 Example Example 16 17 Composition Type and amount of theA-2 A-3 styrene resin 50 60 (% by weight) *1 Type and amount of theblock B-17 B-3 copolymer 50 40 (% by weight) *1 Stabilizer Type of thestabilizer *2 A/D A/C/F Amount of the stabilizer A: 0.3 A: 0.1 (part byweight) *3 D: 0.1 C: 0.1 F: 0.3 Heat shrinkability of the heatshrinkable film 80° C. shrinkage factor (%) 72 75 Natural shrinkagefactor   0.4   0.2 (%) Resistance to fusion 602 602 bonding in hot water

INDUSTRIAL APPLICABILITY

[0165] A shaped article (such as a sheet) produced from the blockcopolymer, block copolymer composition or block copolymer/styrene resincomposition of the present invention not only is free from markedoccurrence of FE's (fish eyes), but also has excellent stiffness,elongation, impact resistance, transparency and heat shrinkability.Therefore, the block copolymer or composition of the present inventioncan be advantageously used in various application fields. For example,the block copolymer or composition of the present invention can bemolded by injection molding, blow molding or the like to obtain acontainer for parts of office automation apparatuses, daily commodities,food, miscellaneous goods, parts of light electric appliances and thelike. Especially, it is advantageous to use the block copolymer orcomposition of the present invention for producing a thin film (such asa heat shrinkable film or a laminate film), a transparent sheet (such asa blister case for food or parts of light electric appliances) and thelike.

1. A block copolymer comprising: at least two S polymer blocks, eachcomprising at least 70% by weight of vinyl aromatic hydrocarbon monomerunits, and one or more B polymer blocks selected from the followingpolymer blocks (a), (b) and (c): (a) a polymer block comprising isoprenemonomer units or comprising isoprene monomer units and vinyl aromatichydrocarbon monomer units, (b) a polymer block comprising 1,3-butadienemonomer units or comprising 1,3-butadiene monomer units and vinylaromatic hydrocarbon monomer units, and (c) a polymer block comprisingisoprene monomer units and 1,3-butadiene monomer units or comprisingisoprene monomer units, 1,3-butadiene monomer units and vinyl aromatichydrocarbon monomer units, wherein the content of the vinyl aromatichydrocarbon monomer units in each of said polymer blocks (a) to (c) isless than 70% by weight, wherein said one or more B polymer blocks arecomprised of one system selected from the group consisting of (B-1) to(B-5): (B-1) at least one polymer block (a) and at least one polymerblock (b) in combination, (B-2) at least one polymer block (a) and atleast one polymer block (c) in combination, (B-3) at least one polymerblock (a), at least one polymer block (b) and at least one polymer block(c) in combination, (B-4) at least one polymer block (b) and at leastone polymer block (c) in combination, and (B-5) at least one polymerblock (c) alone, the amount of the vinyl aromatic hydrocarbon monomerunits in said block copolymer and the total amount of the isoprenemonomer units and the 1,3-butadiene monomer units in said blockcopolymer being, respectively, from 60 to 95% by weight and from 40 to5% by weight, each based on the weight of said block copolymer, saidblock copolymer having an isoprene monomer unit/1,3-butadiene monomerunit weight ratio of from 45/55 to 97/3, and wherein the vinyl aromatichydrocarbon monomer unit moiety of said block copolymer has a shortsegment ratio of from 0 to 30% by weight, wherein said short segmentratio is defined as the weight percentage, based on the total weight ofvinyl aromatic hydrocarbon monomer units contained in said blockcopolymer, of the vinyl aromatic hydrocarbon monomer units contained inat least one short segment consisting of 1 to 3 vinyl aromatichydrocarbon monomer units.
 2. The block copolymer according to claim 1,which comprises (B-5) at least one polymer block (c) alone as said Bpolymer block.
 3. The block copolymer according to claim 1, whichcomprises (B-1) at least one polymer block (a) and at least one polymerblock (b) in combination as said B polymer block.
 4. The block copolymeraccording to claim 1, wherein said isoprene monomer unit/1,3-butadienemonomer unit weight ratio is in the range of from 55/45 to 95/5.
 5. Theblock copolymer according to claim 1, wherein said short segment ratiois in the range of from 1 to 25% by weight.
 6. The block copolymeraccording to claim 1, which is a linear block copolymer.
 7. A blockcopolymer composition comprising 100 parts by weight of the blockcopolymer of any one of claims 1 to 6 and 0.05 to 3 parts by weight ofat least one stabilizer which is selected from the group consisting of2-(1-(2-hydroxy-3,5-di-t-pentylphenyl)ethyl)-4,6-di-t-pentylphenylacrylate,2-t-butyl-6-(3-t-butyl-2-hydroxy-5-methylbenzyl)-4-methylphenylacrylate, and 2,4-bis((octylthio)methyl)-o-cresol.
 8. A blockcopolymer/styrene resin composition comprising 10 to 99% by weight ofthe block copolymer of any one of claims 1 to 6 and 90 to 1% by weightof a styrene resin.
 9. A block copolymer/styrene resin compositioncomprising the block copolymer composition of claim 7 and a styreneresin, wherein the weight ratio of the block copolymer present in saidblock copolymer composition to said styrene resin is 10/90 to 99/1.